The present invention relates generally to systems and methods for using gated optical detectors in ambient light in order to determine the location or distribution of an induced optical signal in vivo, and more particularly relates to coupling the use of a gated intensified charge-coupled device imaging camera, insensitive to room light, to the use of a targeted fluorescent contrast agent and a synchronized illuminating laser to detect and image cancer cells present in the human body in trace amounts in vivo and in real time, during invasive cancer surgery or guided tumor biopsy, without requiring a darkened operating theater.
Optical imaging systems and methods which provide real-time detection, diagnosis and imaging of diseases such as cancer are known in the art. The application of such systems in vivo during real time medical or surgical procedures has been limited by a poor signal to noise ratio. This low signal to noise ratio is a consequence of the low strength or absence of an optical signal arising from the target tissue, the high level of background noise from any ambient light, and the poor sensitivity and specificity of the detected optical signal.
The magnitude of the signal to noise problem is best appreciated by considering that the reflected irradiance from tissue surfaces in an operating room can be as high as 10 mW/cm2, or more, under the brilliant surgical headlamps and overhead spotlights. Under normal operating room illumination, this translates into 1018 (1 billion billion) photons reflected from each square centimeter of tissue per second. In contrast, the native fluorescence may be on the order of 107 below the incident light, about 109 photons/cm2/sec, or less. This makes the detection of trace amounts of disease difficult in ambient light. Using the photon counts in the example just described, the ambient light is one billion fold greater per square centimeter than the detectable native fluorescent signal from a 1 mm tumor, or one trillion fold greater per square centimeter than the signal from a 100 micron tumor. Complicating matters further, some target tissues or disease conditions have a signal that is non-specific, or may have no detectable optical signal at all.
Detection of trace amounts of target tissue in room light therefore requires that the signal to noise ratio be improved beyond what is currently taught in the art, in the range of 104 to 109 fold improvement, either by reducing the noise introduced by background ambient light, or by increasing the strength and specificity of the target signal, or both.
With regard to improving the signal to noise through the rejection of ambient light, the majority of known optical diagnostic systems and methods simply ignore, background subtract, or turn off room light. Examples include most invasive devices equipped with optics, such as catheters, needles, and trocars (e.g., U.S. Pat. No. 5,601,087), as well as noninvasive devices for imaging or measuring the optical features of living tissue externally (e.g., U.S. Pat. Nos. 5,936,731, WO 98/10698, Sweeny et al. in Proc. Natl. Acad. Sci. 1999;96(21):12044-12049, Weissleder et al. in Nature Biotech 1999;17:375-378). However, turning off the lights or obscuring a view of the patient using dark drapes during a medical procedure is disadvantageous and possibly dangerous, especially during critical surgical procedures. On the other hand, simply ignoring or background subtracting ambient light risks overflowing the detector and/or burying weak signals from trace amounts of tissue in the background noise. Thus, such simplistic approaches diminish the possibility of real-time feedback during medical procedures, unless the ambient light is specifically rejected.
Schemes for the true rejection of ambient light are known, and include the use of band pass filters, temporal signal modulation, and lifetime analysis. However, such methods often fail in ambient light. For example, a bandpass filter wide enough to pass the bulk of a biological fluorescent signal in vivo will still pass at least 5% of the ambient light as well, far short of the needed 104 to 109 enrichment in signal to noise required to unmask a weak native fluorescence. Temporal methods can be arranged to provide background rejection in tissue imaging, however approaches such as amplitude modulation (e.g., U.S. Pat. Nos. 5,213,105, 5,648,269, and 5,865,754) and time-of-flight measurement (e.g., U.S. Pat. No. 5,919,140, WO 98/10698) have historically been configured instead to measure temporal information about the time required for photons to traverse a tissue or leave a fluorescent molecule, rather than to reject ambient signal. In addition, such temporal schemes work well only when the target signal is sufficiently strong that a temporal response (time-of-flight rise or fall time, phase shift, fluorescence lifetime) can be accurately estimated, and thus fail to operate in real time when only trace amounts of the target tissue are present, or when the ambient light is strong.
All of the above systems and methods fail to reject significant amounts of background radiation, operate only under darkened conditions, require strong target signals, or require long integration times that preclude real-time use, and thus fail to reliably detect trace amounts of a target tissue in the presence of common levels of ambient light.
The above drawbacks notwithstanding, improved ambient light rejection alone may not be sufficient to achieve a real-time system for use in vivo under operating room conditions. Although some large cancers may be detectable using native signals (e.g., U.S. Pat. No. 5,647,368), many physiological and pathological conditions possess no detectable native optical signal, or have only a weak or non-specific optical signature, particularly when trace amounts of disease are to be detected.
Contrast agents have been used in the past for medical monitoring and imaging when the inherent or native signal in vivo is absent or poor. A contrast agent serves to lend a strong, identifiable signal to an otherwise poorly detectable tissue. In this regard, optical contrast agents are known in the art. The majority of known optical contrast agents are untargeted (e.g., U.S. Pat. Nos. 5,672,333, 5,928,627, WO 97/36619, Lam et al. in Chest 1990:97(2):333-337, and Hxc3xcber et al. in Bioconjugate Chem 1998;9:242-249). Such untargeted agents rely largely upon the physical characteristics of the agent, such as solubility in fat versus water, or upon cellular metabolism, to non-specifically partition them into a particular tissue. As untargeted dyes produce widely distributed and nonspecific signals, they require a large stained tissue volume in order to generate a statistically clear signal in vivo, they tend to produce weak signals, insufficiently above background noise, from smaller or trace target tissue volumes. For example, photodynamic therapy agents accumulate in certain cancerous cells (Lam et al., Huber et al.), but they also accumulate in normal tissues. None of the preceding optical contrast methods or devices teach in vivo targeting of rare cells through the use of highly specific targeting agents, and thus will fail for use in the detection of trace amounts of a target tissue in vivo.
A few agents allowing for more localization targeting of dye are known. For instance, Sweeny et al. teach a process of genetically altering cells cultured or grown outside of the body, followed by insertion of these cells into the body for imaging. Such removal and reinsertion of cells may not make sense for use in patients with spontaneous diseases such as cancer, which should not be altered and reintroduced into the patient""s body. Further, as the transformed cells glow continually, there is no inducible component to the light (such as fluorescent light induced using a flash lamp), and therefore little if any enhancement is possible through use of gated rejection of ambient light. Weissleder et al. (Nature Biotech 1999;17:375-378) teach another dye that is targeted in the sense that it is locally activated, while WO 98/48846 suggests multiple methods of creating optical dyes for use in vivo. Each of these approaches is realized without provision for the specific rejection of ambient light though use of a gated detector, and thus will fail for use in the detection of trace amounts of a target tissue in vivo and in the presence of ambient light.
In summary, none of the preceding approaches suggest gating the detector to substantially reject ambient light, nor do they suggest combining a gated ambient-light-insensitive imager, a high-power synchronized light source, and highly-specific tissue-targeted contrast agent into a cohesive system for detecting and imaging trace amounts of target tissue in room light. Therefore, device and methods taught in the present art will fail in many cases to detect and localize trace disease such as small primary cancers, early metastatic disease, local inflammatory conditions, or unstable coronary wall plaque, in vivo and in real time under ambient light conditions. A real-time optical system and method to detect or image an induced or contrast-influenced target tissue signal in vivo and in ambient light has not been taught, nor has such a tool been successfully commercialized.
What is needed, and not yet suggested or taught, is a method and optical system to detect a signal from trace tissue in vivo and in real time despite the presence of a high level of ambient light, possibly including the step of enhancing a weak native signal (or creating one where one did not previously exist), in order to produce an optical system for detecting, imaging, targeting, and treating of tissue, such as trace amounts of cancer, in vivo and in real time.
The present invention relies upon gating an optical detector or optical imaging camera so as to allow for rapid detection, imaging, localization, or targeting of trace amounts of target tissue in vivo and in real time in the presence of ambient light, with or without the presence of a targeted optical contrast agent.
A salient feature of the present invention is a recognition that ambient light can be substantially rejected ( greater than 104 rejection) by gating the detection or imaging system to be sensitive to light arriving only during specific brief intervals, and that if a native or contrast-influenced target signal is produced with greater intensity during these brief intervals, then such ambient light rejection results in an reduction in the background signal and a relative enrichment of target signal with respect to the ambient light noise.
Another salient feature is that a weak or absent target signal can be enhanced in intensity, specificity, or both through use of a targeted contrast agent, and that optical systems and methods can be used to induce and detect this enhanced contrast signal in synchrony with gated detection, thus again enabling improved real-time detection or imaging during targeted medical procedures and therapies.
Accordingly, an object of the present invention is to provide a system and method to detect, localize, image, or target a selected tissue using optical detection or imaging in ambient light, wherein use of conventional ungated detectors would otherwise have required highly darkened rooms, unacceptably long integration times, or extensive averaging and background subtraction.
Another object is to substantially reject the background ambient light ( greater than 104 rejection), while relatively preserving the target signal, such that the resulting detected light is enriched in target signal with respect to the reduced background light noise.
Another object is that the illumination source may be synchronized with the detector gating, allowing for a high peak illumination power using brief periods of illumination, and resulting in strong induced target signals using a low average illumination power.
Another object is that trace amounts of tissue, such as cancer, vascular disease, neovasculature due to angiogenesis, and infection, can be detected and imaged in real time with a high sensitivity. In some embodiments of the present invention, it may be possible to detect as few as 100 cells or less, in vivo and in real time.
Another object is that a weak or absent tissue signal may optionally be enhanced by use of a targeted optical contrast agent, and that this targeted agent can be induced and detected in conjunction with detector gating, resulting in an improved target tissue signal with respect to background noise. Such optical contrast can be an endogenous tissue component, or can be an exogenous optical contrast agent administered to the subject, followed by a period to allow distribution and localization sufficient for detection or imaging. The contrast agent may be administered in an active form, or as a pre-active pro-drug that requires metabolic activation. The contrast is ideally targeted via a targeting moiety, such as an antibody, antibody fragment, protein or synthetic peptide, or receptor analog, or the contrast may be locally activated or altered via a metabolic processing step, such that the majority of the signal arises from the target tissue with minimal or no enhancement of the surrounding tissues.
Another object is that by combining an ambient-light-insensitive detector or camera, an exogenous targeted contrast agent, and a synchronized illumination source, sufficient enhancement in the target tissue specific signal as compared to the ambient light background signal may occur so as to allow the detected optical signal to reach medical relevance.
Another object is that the targeting moiety of the contrast agent can be altered or changed during manufacture of the agent, such that the specificity and target tissue of the contrast agent can be selected from a menu of many different target tissues, while retaining a substantially similar imaging platform system.
Another object is that the dye moiety of the contrast agent can be altered or changed during manufacture of the agent, such that the wavelength and optical characteristics of the contrast agent can be altered while retaining a substantially similar target tissue and target tissue sensitivity.
Another object is that the detection, localization, or imaging of the target signal can be used to provide feedback during an invasive procedure, to provide control for any process of collection or treatment, such as an ablation process.
Another object is that this monitoring may represent a decision point upon which a human response may be initiated, such as with a visual guidance display or an alarm bell that signals correct placement, or an interlock decision may be initiated when a treatment is complete, such as via an output signal attached to a medical device.
Another object is that localization of an invasive medical instrument with respect to a target tissue can be made. This localization can be in the form of a determination of the distance or direction of the device to the target tissue, or the instrument can be localized in space in one or more dimensions. Such information can be used to make a guidance signal for the purpose of guiding the medical instrument to a target location. Alternatively, the localization can be in the form of a determination of the tissue compartment in which the device is currently placed, such as tumor, normal prostate, residual prostate cells outside of the prostatic capsule, or by tissue type, such as skin, muscle, or blood vessel.
Another object is that system and method can be enhanced by concurrent or a priori knowledge, such as the known optical spectral characteristics of target tissues or tissues expected to be encountered during placement (which can be stored for reference in the device or in the instrument), the area of the body the physician is working (such that far away tissues need not be considered in the analysis), or information from other medical scans (such as a CT or MRI scan). This optical approach may be combined with other real-time approaches, such as a combination of an ultrasound probe and an optical instrument to produce an overlay of an optical image upon a standard ultrasound image. Such a combination would provide both structural (ultrasound) and biochemical (optical) images simultaneously.
Another object is that the detection, localization, or imaging information can be presented to the user in a number of ways, such as an image processed for ease of interpretation, a displayed word describing progress, a variable alarm to indicate the progress of treatment of a tumor through changes in pitch or speed or intensity of the tones, or other manners of presentation, in such a way as to allow the user to gain an incremental understanding of the progress of the procedure or therapy.
Another object is that detection system can be used in animal research to provide noninvasive monitoring of physiologic, pathologic, or pharmaceutical processes, such as tumor growth under treatment by chemotherapeutic agent, with one or more of the following goals: reducing animal usage, improving data quality, shortening test cycles, reducing costs of development, collecting data for FDA or quality control purposes, and/or for research and testing of pharmaceuticals.
A final object is that the detection or imaging system is sufficiently sensitive that embodiments within the spirit of the invention can be used for relatively longer integration times to detect disease buried deep within the human body, at a possible cost of losing real time feedback, in cases where conventional monitoring or imaging systems may lack the specificity, such as bone scans and screening of deep scar tissues for sites of cancer recurrence.
The systems and methods as described have multiple advantages. One advantage is that the system can be used in room light during surgery, in vivo and in real time. Another advantage is the production of images in real-time, even for tissues that are present in trace amounts. Another advantage is that the system as described is a platform system, with the target tissue changeable at the time of manufacture of the contrast agent. Another advantage is that the system may allow reduction of animal use or length of studies in animal research. A final advantage is that the system, by virtue of a high specificity, may have application to use in vivo for the detection of deeply buried processes, though integration times may be long and the real time aspect of the present invention may be lost.
There is provided a system for monitoring or imaging optical characteristics of tissue in the presence of ambient light, with or without the presence of a signal-enhancing targeted optical contrast agent. In one example, the system has a gated digital imaging camera, optically coupled to the tissue through lenses and filters, placed above the operating field, and a laser light source that illuminates the tissue and which is synchronized with the gated camera. The camera detects a portion of the laser light that has passed through the tissue and interacted with a contrast agent in vivo. Use of a contrast agent improves the sensitivity of the system by enhancing a weak or absent signal from the target tissue. The gated detector enhances the sensitivity of the system by rejecting a significant fraction of the background ambient light, while preserving signal from the contrast agent. A computer controls the light source and gated camera, and receives a signal from the gated detector, which may be stored in memory. An image processor receives a signal representing raw data from the computer and provides a contrast localization image, used to identify and image a target tissue, to target a medical instrument or therapy toward a particular site in the body, to determine the accuracy of placement of an invasive instrument, or to provide a feedback signal to the user regarding therapy progress. A method of imaging a contrast agent in tissue in the presence of ambient light is also described.
The breadth of uses and advantages of the present invention are best understood by example, and by a detailed explanation of the workings of a constructed apparatus, now in operation and tested in model systems, tissue culture, and in animals, and humans. These and other advantages of the invention will become apparent when viewed in light of the accompanying drawings, examples, and detailed description.